In accordance with an embodiment, described herein is a system and method for supporting JavaScript activities in an executable process defined by a process execution language. A JavaScript activity can be added to the executable process using attributes defined in an extension namespace to the process execution language. A process execution engine, with an embedded JavaScript engine, can be provided in a SOA middleware environment, to interpret JavaScript artifacts within the JavaScript activity and to provide contextual information, states and payloads of variables in the executable process. Within the JavaScript Activity, JavaScript code can be used to access a plurality of custom JavaScript objects; XPath functions and custom functions defined by the process execution language; and different types of variables in the executable process. JavaScript code can also be used to manipulate these variables using the XPath functions and custom functions accessible within the JavaScript activity.